Battery bank and inverter options

solargirl · February 2010

Re: Battery bank and inverter options

I think I have posted this before, My husband had a list of things to do and one of them was to check into a IOTA 48 volt charger... Maybe I should do that too. ??

halfcrazy · February 2010

Re: Battery bank and inverter options

Solargirl if you are really looking for a new inverter go with the XW line as has been discussed and it has a great battery charger. My issue with the iota chargers is they are expensive and don't go as high in voltage as I would like. Plus no equalize feature. I would say spend the money on an XW inverter and a Midnite solar Epanel to go with it and don't bother with the Iota's

BB. · February 2010

Re: Battery bank and inverter options

The XW has a 100 amp charger which would work nicely with your 120/240 VAC genset (I think the XW needs a 240 VAC genset to charge properly--a 120 VAC only connection will not work). XW will be very nice as the primary charger (when running with the Genset). Your SW 4048 only has a 60 amp maximum current capable charger.

The Crown 1,381 AH bank * 5% minimum recommended charge = 69 amps minimum...

100 amps / 1,381 battery capacity = 0.072 = 7.2 % charging--The XW 6048 is a better match for your bank.
100 Amps * 58 volts charging * 1/0.89 eff charger = 6,517 watts AC input from genset
6,517 XW charger load / 20,000 watt genset = 0.33 = 33% generator load

If your current genset is worn out (earlier in thread?)--and you are not going to rebuild--You should look at a 10-15kW diesel unit.

Just using some of the data from the Hardy Solar diesel generator website--To pick some numbers and see if they make sense with your existing setup... 403D-11G engine with 9kW 1,800 RPM prime rated alternator: fuel flow of 3/2.3/1.7 liters per hour at 100%/75%/50% of rated load. The 404D-22G rated at 19.2 kWatt 1,800 RPM; fuel flow of 4.3/3.4/2.4 liters per hour...

Assume your old system ran 60 amps at 58 volts and 80% efficiency:

60a * 58v * 1/0,80 = 4,350 watts

And your 20 kW genset is running at 4.35kW/20 kW = 0.22 = 22% of capacity. Fuel Flow would be for 50% rated load or less of:

2.4 liters/hour * 1/3.79 l/gallon =0.63 gallons per hour (20 kW running SW 4048 charging)

The 10 kW genset would be running at 6,517 watts / 9,000 watts = 72,4% of rated power--So;

2.3 liters/hour * 1/3.79 l/gallon =0.61 gallons per hour (10 kW running xW 6048 charging)

The fuel efficiency difference between running the SW 4048 on a 20 kW genset vs a XW 6048 on a 10 kW genset figured in kWhrs per gallon of diesel:

60 amps * 58 volts * 1k/1,000 watt * 1/0.63 gph = 5.5 kWhr / gallon SW and 20 kW
100 amps * 58 volts * 1k/1,000 watts * 1/0.61 gph = 9.5 kWhr / gallon XW and 10 kW
9.5 kWhr/gal / 5.5 kWhr/gal = 1.72 x more fuel efficient
1/1.72 = 0.58 or 58% of the amount of fuel you are currently using

The above math is very approximate--and used to demonstrate a point about how to figure out and justify the appropriate sized generator to your loads.

If you have other loads (such as well pump/Air Conditioning/etc.) that you run with your diesel genset, then the 20kW may be a better match for you.

But, if you use it most of the time to charge your battery bank (with just the SW or XW units)--then you could get a substantially smaller unit and save some money and fuel costs.

The above numbers are guesstimates -- your actual numbers may vary. Work with your genset supplier to decide on the optimum unit for your home.

I just re-read through your I need help thread... I think the XW 6048 will be a nice fit for your home and genset. (I don't want to redo the rest of the "I need help" stuff and create any confusion). Just make sure you are not running the generator to charge the battery bank above ~90% (unless you are using the genset to equalize)--your fuel efficiency and generator life is much better with a 50-60%+ electrical load.

At the time, I would not suggest the 48 volt Iota 15 amp charger--The largest ones they sell are in the 15-20 amp range--Your "backup charger" would need to be in the 70-140 amp range--The IOTA way too small to be of much use for you.

Perhaps, you can locate a used (or new) 48 volt battery fork lift charger that is compatible with your genset capacity (existing or new).

-Bill

mike95490 · February 2010

Re: Battery bank and inverter options

> The 10 kW genset would be running at 6,517 watts / 9,000 watts = 72,4% of rated power

Diesel Gensets should be run at least at 50% power. Less than that invites ring and bore glazing. the 10KW sounds like it's the right size.

solargirl · February 2010

Re: Battery bank and inverter options

BB. wrote: »

The XW has a 100 amp charger which would work nicely with your 120/240 VAC genset (I think the XW needs a 240 VAC genset to charge properly--a 120 VAC only connection will not work). XW will be very nice as the primary charger (when running with the Genset). Your SW 4048 only has a 60 amp maximum current capable charger.

The Crown 1,381 AH bank * 5% minimum recommended charge = 69 amps minimum...
100 amps / 1,381 battery capacity = 0.072 = 7.2 % charging--The XW 6048 is a better match for your bank.

100 Amps * 58 volts charging * 1/0.89 eff charger = 6,517 watts AC input from genset

6,517 XW charger load / 20,000 watt genset = 0.33 = 33% generator load

If your current genset is worn out (earlier in thread?)--and you are not going to rebuild--You should look at a 10-15kW diesel unit.

Just using some of the data from the Hardy Solar diesel generator website--To pick some numbers and see if they make sense with your existing setup... 403D-11G engine with 9kW 1,800 RPM prime rated alternator: fuel flow of 3/2.3/1.7 liters per hour at 100%/75%/50% of rated load. The 404D-22G rated at 19.2 kWatt 1,800 RPM; fuel flow of 4.3/3.4/2.4 liters per hour...

Assume your old system ran 60 amps at 58 volts and 80% efficiency:
60a * 58v * 1/0,80 = 4,350 watts

And your 20 kW genset is running at 4.35kW/20 kW = 0.22 = 22% of capacity. Fuel Flow would be for 50% rated load or less of:
2.4 liters/hour * 1/3.79 l/gallon =0.63 gallons per hour (20 kW running SW 4048 charging)

The 10 kW genset would be running at 6,517 watts / 9,000 watts = 72,4% of rated power--So;
2.3 liters/hour * 1/3.79 l/gallon =0.61 gallons per hour (10 kW running xW 6048 charging)

The fuel efficiency difference between running the SW 4048 on a 20 kW genset vs a XW 6048 on a 10 kW genset figured in kWhrs per gallon of diesel:
60 amps * 58 volts * 1k/1,000 watt * 1/0.63 gph = 5.5 kWhr / gallon SW and 20 kW

100 amps * 58 volts * 1k/1,000 watts * 1/0.61 gph = 9.5 kWhr / gallon XW and 10 kW

9.5 kWhr/gal / 5.5 kWhr/gal = 1.72 x more fuel efficient

1/1.72 = 0.58 or 58% of the amount of fuel you are currently using

The above math is very approximate--and used to demonstrate a point about how to figure out and justify the appropriate sized generator to your loads.

If you have other loads (such as well pump/Air Conditioning/etc.) that you run with your diesel genset, then the 20kW may be a better match for you.

But, if you use it most of the time to charge your battery bank (with just the SW or XW units)--then you could get a substantially smaller unit and save some money and fuel costs.

The above numbers are guesstimates -- your actual numbers may vary. Work with your genset supplier to decide on the optimum unit for your home.

I just re-read through your I need help thread... I think the XW 6048 will be a nice fit for your home and genset. (I don't want to redo the rest of the "I need help" stuff and create any confusion). Just make sure you are not running the generator to charge the battery bank above ~90% (unless you are using the genset to equalize)--your fuel efficiency and generator life is much better with a 50-60%+ electrical load.

At the time, I would not suggest the 48 volt Iota 15 amp charger--The largest ones they sell are in the 15-20 amp range--Your "backup charger" would need to be in the 70-140 amp range--The IOTA way too small to be of much use for you.

Perhaps, you can locate a used (or new) 48 volt battery fork lift charger that is compatible with your genset capacity (existing or new).

-Bill

Hi Bill,

Thankyou for all this info, The generator is not wore out yet.... It has 7000 hours on it, I meant the charger on the inverted is wore out.

(sorry I am not very technical), I can run the generator charging or equailizing the batteries for about 8 hours give or take on 5 gal of diesel.

It is getting late and I will re-read the post in the a.m. when I have half a brain.

Thankyou again for being so helpful.

Solargirl

BB. · February 2010

Re: Battery bank and inverter options

SolarGirl,

Not a problem--I obviously miss stuff too...

I would really like to know what your typical discharge of the battery bank is... I saw 4-6 amps 24/7...

Let us assume 5 amps @ 48 volts for 24 hours. Run some math and see how things look:

5 amps * 24 hours = 120 AH
120 AH / 1,381 AH battery = ~9% discharge per day
120 AH * 48 volts = 5,760 Watt*Hours = 5.76 kWhrs per day from battery
5,760 Watt*Hours * 0.85 inverter efficiency = 4,896 WH = 4.9 kWhrs per day of 120/240 VAC power

The above looks very reasonable--you can run the battery for ~3 days between charging (no sunlight, no genset) very nicely (72% state of charge).

It would be nice to have a battery monitor (you may already have one--I am not sure) to confirm the above readings (there is a difference between seeing ~4-6 amps every time you look at a meter versus a totalizing AmpHour meter that does this electronically).

Now--your ~5 gallons of diesel per day (assuming no sun?)--Your diesel is very capable of 5-10kWhrs per gallon of fuel--So, at first glance, you are using 2-10x as much fuel as you should be with your current setup (excluding the contribution by your solar panels).

And, on a sunny day--your 20x175Watt of solar panels should be able to run pretty much 100% of your loads (5amp average) on two hours of "full" sun per day.

So, lets start with the solar panels... Using the PV Watts website. For Bakersfield CA, 3.5 kWatts of solar panels (20x175w), use derating of 0.52 (assuming 80% eff flooded cell and 85% eff inverter).

"Station Identification"
"City:","Bakersfield"
"State:","California"
"Lat (deg N):", 35.42
"Long (deg W):", 119.05
"Elev (m): ", 150
"PV System Specifications"
"DC Rating:"," 3.5 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 1.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 35.4"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.47, 182, 22.75
2, 4.64, 216, 27.00
3, 5.63, 288, 36.00
4, 6.44, 316, 39.50
5, 6.78, 330, 41.25
6, 7.31, 335, 41.88
7, 7.28, 341, 42.62
8, 7.30, 347, 43.38
9, 6.90, 327, 40.88
10, 6.19, 310, 38.75
11, 4.67, 232, 29.00
12, 3.21, 164, 20.50
"Year", 5.82, 3390, 423.75

Take the lowest month of December at 164 kWhrs per month for 3.5 kW of solar panels or:

164kWhrs per month / 30 days per month = 5.47 kWhrs per day

So--Even in December. on average, you should need not need the run the genset very much (just during stretches of cloudy weather).

Because you are using a Fork Lift battery--they can take very high charge rates... From the Crown Battery Site regarding charging:

Opportunity Rapid Charge

New charger technology has been developed to allow batteries to be charged faster and at substantially higher charge rates, called Opportunity Rapid Charging or Fast Charging. Opportunity charging is charging the battery at every opportune time possible. The battery should be charged at breaks, lunches, and at the end of each shift and any other times when the battery can be charged for at least 10 minutes. Rapid charging is defined as charging the battery from 20% to 80% state of charge in two hours or less. By opportunity charging the battery the state of charge is maintained between 30% and 80% during the normal work shift. Once a day, the battery is allowed to recharge to 100% of its rated capacity. On weekends, the battery will be automatically equalize charged while it is still connected to the charger. Opportunity Rapid Charging can only be safely accomplished with a specially designed charger with sophisticated control capable of monitoring battery conditions.

So--if you allow the battery to discharge down to below 80% state of charge--you can recharge at a rate of:

80%-20%=60% capacity
60% capacity / 2 hour charge = 30% charge rate
1,381 AH battery * 30% Charge Rate = 414 amps
414 amps * 58 volts * 1/0.80 charger eff = 30,000 watts = 30 kW

Well--that is way higher charge rate than you can do (or want to pay for). But that gives us a "high limit" for the battery bank.

For your 20 kW genset--you would, ideally want to run the unit at 50% - 75% of rated capacity:

20,000 watts * 0.50 capacity * 1/58 volts * 0.80 charger eff = 138 amps for fuel efficient charging
20,000 watts * 0.75 capacity * 1/58 volts * 0.80 charger eff = 207 amps maximum load for 20k Genset

The XW 6048 can output 100 amps--so if you could find another charger in the 40-100 Amp range (needs to be power factor corrected) to pair with your XW inverter/charger would be nice...

Once your battery is >85% state of charge, the current will need to be brought way down--and this is the time to allow your solar array to finish off the battery charging (don't bother with the genset--waste of fuel).

So--Your "normal" daily operation would be:

run off of solar day to day
if battery state of is below 75% state of charge and bad weather is forecast--you can start the genset the next morning (say ~7am or 8am). Run genset until state of charge is over 80-85%.
if battery state of charge is below 50% state of charge, start genset immediately--run genset until state of charge is over 80-85%
a fully charge bank is over > 90% state of charge... Don't run the genset to try for 100% unless you are trying to equalize and the solar array is not enough.
only equalize when needed... For example when cell specific gravity ranges are further than 0.030 apart (or roughly >0.030 volts per cell difference). Only equalize until the SG stops rising (over a 30-60 minute period).

Ideally, with your 60 amp SW 4048 inverter/charger--Assuming ~5amps * 24 hours per day and only starting the genset below 75% state of charge--you would be running the genset:

5 amps * 24 hours * 1/60 amps = 2 hours per day (assuming dark weather)
1,381 AH * 0.10 * 1/60 amps = 2.3 hours per 10% increase in battery charge (say 70%-80% state of charge).

And, at these power levels, I am guessing your 20 kW genset will run its fuel consumption at ~0.63 gallons per hour (remember to stop charging at ~80-85% state of charge--bulk charging can take 100% of your generator/inverter charger current):

2 hours * 0.63 gph = 1.26 gallons (SW 4048 per "dark" day)
2.3 hours * 0.63 gph = 1.45 gallons (SW 4048 per 10% battery charge)

The same numbers running an XW 6048 100 amp charger:

5 amps * 24 hours * 1/100 amps = 1.2 hours per day (assuming dark weather)
1,381 AH * 0.10 * 1/100 amps = 1.4 hours per 10% increase in battery charge (say 70%-80% state of charge).

And, same as above, but using 100 amps for the XW 6048 inverter/charger:

1.2 hours * 0.63 gph = 0.75 gallons (XW 6048 per "dark" day)
1.4 hours * 0.63 gph = 0.88 gallons (XW 6048 per 10% battery charge)

And for the solar panels (3.5 kW), for every 10% increase in state of charge--December:

164 kWhrs per month * 1/30 days = 5.46 kWhrs per day = 5,460 WH
1,381 AH * 0.10 * 58 volts charging * 1/5,460 WH per day = 1.5 days (December)

And for the solar panels (3.5 kW), for every 10% increase in state of charge--For much of the rest of the year (April-October) where you get >300 kWhrs per month:

300 kWhrs per month * 1/30 days = 10.0 kWhrs per day = 10,000 WH
1,381 AH * 0.10 * 58 volts charging * 1/10,000 WH per day = 0.8 days (or faster)

The above numbers are estimates--but should give you a good idea of how your system compares.

Hope this makes sense.

-Bill

Battery bank and inverter options

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